Atomic Structure and the Periodic Table Flashcards
proton
positively charged particle found in the nucleus of an atom
relative mass:1
charge:+1
neutron
particle with zero charge found in the centre of the atom
relative mass:1
charge:0
electron
negatively charged particles found on energy levels (shells) surrounding the nucleus inside atoms
relative mass: very small
charge:-1
-move around nucleus in electron shells
-negatively charged + small, but cover a lot of space
-the volume of their orbits determines the size of the atom
-virtually no mass
in an ATOM
number of protons =
number of electrons
-charges cancel out
-atoms are neutral (no charge overall)
mass number
top number
-mass of element
-total number of protons and neutrons in the atom
atomic number
bottom number
-number protons in an atom (therefore number of electrons)
element
a substance made up of atoms that all have the same number of protons in their nucleus
a substance containing only one type of atom
isotopes
atoms of the same element with the same number of protons but a different number of neutrons
(same atomic number but different mass numbers)
compound
two or more elements chemically bonded in fixed proportions
diatomic
travels rounds as a pair of atoms
relative atomic mass (Ar)=
relative atomic mass (Ar)=sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes
The average mass of atoms on an element taking into account the mass and amount of each isotope it contains
nucleus
central part of the atom containing protons and neutrons
-in the middle of the atom
-contains protons and neutrons
-positive charge due to the protons
-almost the whole mass of the atom is concentrated in the nucleus
ions
An electrically charged particle containing different numbers of protons and electrons
number of protons ≠ number of electrons
-it has an overall charge
atom
a particle with no electrical charge made up of a nucleus combining protons and neutrons and surrounded by electrons
energy level (shell)
the region an electron occupies surrounding the nucleus inside an atom
in most atoms, the outer shell is not full and this makes the atom want to react to fill it
electronic structure
the arrangement of electrons in the energy levels of an atom
group
the name given to each column in the periodic table
period
the name given to a row in the periodic table
alkali metals
the elements in group 1 of the periodic table
noble gases
the elements in group 0 of the periodic table
halogens
the elements in group 7 of the periodic table
halides
compounds made from group 7 elements
mixture
more than one substance that are not chemically bonded
solvent
the liquid that a solute dissolves in
solution
a solute dissolved in a solvent
soluble
a substance that will dissolve
insoluble
a substance that will not dissolve
solute
the solid that dissolves in a solvent
filtration
separates insoluble solids from liquids
evaporation
separate soluble solids from solutions
-pour solution into evaporating dish
-slows heat the solution - the solvent will evaporate and the solution will get more concentrated. eventually crystals will start to form.
- keep heating the evaporating dish until all you have left are dry crystals
can only be used if the salt doesn’t decompose (break down) when heated
crystallisation
separate soluble solids from solutions
- pour solution into evaporating dish and gently heat - some of the solvent will evaporate and the solution will get more concentrated
-once some of the solvent has evaporated or you see crystals start to form, remove the dish from the heat and leave the solution to cool
-the salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
-filter the crystals out of the solution and leave them in a warm place to dry
history of the atom
solid spheres
plum pudding model
nuclear model - Rutherford (alpha particle scattering experiment)
nuclear model - Bohr
Rutherford - existence of protons
James Chadwick - existence of neutrons - model of the atom close to nowadays nuclear model
plum pudding model
J J Thomson
ball of positive charge with electrons stuck in it
nuclear model
Rutherford
tiny, positively charged nucleus at the centre, where most of the mass is concentrated. A ‘cloud’ of negative electrons surround the nucleus - most of the atom is empty space
-conducted alpha particle scattering experiments
-fired positively charged alpha particles at an extremely thin sheet of gold-expected to pass straight through the sheet or be slightly deflected at most
-when alpha particles came near the concentrated, positive charge of the nucleus, they were deflected
- if they were fired directly at the nucleus, they were deflected backwards
-otherwise, they passed through the empty space
Bohr’s nuclear model
scientists realised that electrons in a ‘cloud’ around the nucleus of an atom, as Rutherford described, would be attracted to the nucleus, causing the atom to collapse
suggested that all electrons were contained in shells
- electrons orbit the nucleus in fixed shells and aren’t anywhere in between
- each shell is a fixed distance from the nucleus
methods mixtures can be separated
chromatography
filtration
crystallisation
simple distillation
fractional distillation
simple distillation
used to separate a liquid from a solution
-solution is heated, part with lowest boiling point evaporates first
-vapour is cooled, condenses, and is collected
-rest of solution is left behind in the flask
can be used to separate salt and sea water
problem is can only be used to separate things with very different boiling points - if the temperature goes higher than the boiling point of the substance with the higher boiling point, they’ll mix again
fractional distillation
used to separate a mixture of liquids
-put mixture in flask and stick a fractionating column on top and heat it
-the different liquids have different boiling points - evaporate at different temps
-liquid with lowest boiling point evaporates first - when the temp on the thermometer matches the boiling point, it will reach the top of the column
-liquids with higher boiling points will start to evaporate, but the column gets cooler towards the top so will only get part of the way before condensing and running back towards the flask
-when the first liquid has been collected, you raise the temperature until the next one reaches the top
chromatography
used to separate different dyes in ink
-draw a line in pencil (insoluble and won’t dissolve in the solvent) near the bottom of a sheet of filter paper
-add a spot of ink to the line and place the sheet in a beaker of solvent e.g. water
-make sure your ink isn’t touching the solvent otherwise is may dissolve
-put a lid on top of the contained to prevent it from evaporating
-solvent seeps into the paper, carrying the ink with it
-each different dye in the ink will move up the paper at a different rate so will separate out + each will form a spot in a different place
-if any of the dye’s are insoluble they will stay on the baseline
-when the solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry
-the end result is a pattern of spots called a chromatogram
how was the periodic table previously categorised
their physical and chemical properties
their relative atomic mass
how did Dmitri Mendeleev order the periodic table
left gaps and predicted new elements
-mainly in order of atomic mass but switched that order if the properties meant it should be changed
-organised elements with similar properties into the same group
-gaps were left to make sure that elements with similar properties stayed in the same groups. some indicated undiscovered elements + allowed Mendeleev to predict what their properties might be
discovery of isotopes supported this - to not place elements in a strict order of atomic mass but to take account of their properties - isotopes of the same element have different atomic masses but the same chemical properties so occupy the same position on the periodic table
modern periodic table
100ish elements
elements laid out in order of increasing atomic (proton) number - arranging the elements like this means there are repeating patterns in the properties of the elements
metals - left
non-metals - right
vertical columns - groups. group number tells you how many electrons are in the outer shell
rows - periods-each new period represents another full shell of electrons
metals
elements which can form positive ions when they react
towards the bottom and left of the periodic table
left - don’t have many electrons to remove
bottom - have outer electrons which are a long way from the nucleus so feel a weaker attraction
BOTH of these mean that not much energy is needed to remove the electrons
metallic bonding - have similar basic physical properties
-strong
-malleable
-great conductors of heat and electricity
-high melting and boiling points
non-metals
don’t generally from positive ions when they react
at far right and top of periodic table
forming positive ions is much more difficult
right - lots of electrons to remove to get a full outer shell
top - outer electrons are close to the nucleus so feel a strong attraction
far more feasible for them to gain or share electrons to get a full outer shell
no metallic bonding
-dull looking
-brittle
-aren’t always solids at room temp
-don’t generally conduct electricity
-lower density
transition metals
between group 2 and 3
centre of the periodic table
-typical metals and have the expected properties of metals
-they also have:
-can have more than one ion
-transition metal ions are often coloured
-transition metal compounds make good catalysts
group 1 elements
the Alkali metals - reactive, soft metals
one electron in outer shell - very reactive + gives them similar properties
- low density
trends as you go DOWN the group:
increasing reactivity - outer electron is more easily lost as the attraction between the nucleus and electron decreases, because the electron is further away from the nucleus the further down the group you go
lower melting and boiling points
higher relative atomic mass
only ever react to form ionic compounds with non-metals (transfer of electrons)
need little energy to lose an electron and form 1+ ions
more reactive than transition metals - more vigorous
- much less dense, strong, and hard than transition metals + have lower boiling points
alkali metals reaction with water
when Group 1 metals are put in water, they react vigorously to produce hydrogen gas and metal hydroxides - compounds that dissolve in water to produce alkaline solutions
2Na (s) + 2H 2 O (l) → 2NaOH (aq) + H 2 (g)
sodium + water → sodium hydroxide + hydrogen
- the more reactive (lower down the group), the more violent the reaction
- amount of energy released by the reaction increases down the group
alkali metals reaction with chlorine
Group 1 metals react vigorously when heated in chlorine gas to form white metal chloride salts
as you go down the group, reactivity increases so the reaction with chlorine gets more vigorous
alkali metals reaction with oxygen
form a metal oxide
- different types will form depending on the Group 1 metal
Lithium → lithium oxide
Sodium → mixture of sodium oxide and sodium peroxide
Potassium → mixture of potassium peroxide and potassium superoxide
group 7 elements
Halogens
non-metals with coloured vapours
as you go DOWN the group:
-become less reactive - it’s harder to gain an extra electron, because the outer shell’s further from the nucleus
- have higher melting and boiling points
- have higher relative atomic masses
can form molecular compounds - can share electrons with other non-metals via covalent bonding to achieve a full outer shell
form ionic bonds with metals - 1- ions called halides when they bond with metals
more reactive halogens will displace less reactive ones (displacement reaction)
group 0 elements
the Noble Gases - inert, colourless gases
eight electrons in outer shell (except helium which has 2) - full outer shell
- stable - don’t react with much at all
exist as monatomic gases - single atoms not bonded to each other
non-flammable
as you go DOWN the group:
-boiling point increases - greater number of electrons in each atom leading to greater intermolecular forces between them which need to be overcome
